Hi there, does anyone know how long a 98' 4.0L should hold it's fuel pressure? I checked mine tonight and it started at 62lbs in an hour the pressure dropped to 34lbs and 25lbs in one and half hours. Stopped checking after that. Before I checked the pressure I pulled the plugs on bank 2 ,plugs #4 and #6 were wet, smelled like gas. Plug #5 had carbon on it, but it was dry. I have been having getting code 1151 on bank 2, and fuel mileage is down. Could it be I have some bad injectors? Any other ideas?

I had pulled all the plugs about a month ago, and replaced the ones on bank 2, the ones on bank 1 looked like new. I pulled plug #2 again tonight, still looked like new.

 

The fuel pressure should hold within 5psi for at least a minute after the pump shuts off.

Code 1151 is a lean code. Some possible causes:

- Air leaks after the MAF
- Restricted air inlet
- Vacuum hose leaks
- PCV system leaks
- EGR system leaks
- Exhaust leaks before or near the HO2S(s)
- Intake gasket leaks

 

Sounds to me like you might have more than one problem here.

As Rockledge said, the 1152 is a lean O2 code & on a 4.0L of this vintage, a unmetered intake side vacuum leak could cause it.

The wet #4 & 6 plugs that smell like gas, could be from weeping injectors, so why not try a good injector cleaner like Chevron's Techron Consentrate, in a tank of Chevron gas & see how things go with the injectors.

The lower intake manafold gasket bolts are known to loosen up on the 4.0L & cause the lower intake manafold gasket to leak unmetered air & set lean codes.

So if thats the case, maybe re~torquing the lower intake manafold bolts would work. if the gasket hasn't been sucked in.

Also with this vintage, leaking vacuum hoses are always a good possibility too as Rockledge has pointed out.

A dirty MAF sensor from a mis fitted air filter or buttoned up air box is a possibility for causing a lean code too.
Some folks have recently reported fitment problems with Purolater air filters, so if you are using that brand or one made by them & have changed your air filter recently, double check it's fit in the air box.

Just some additional thoughts for consideration.

 

I just recently re-torqued the lower intake. Cleaned the MAF. I'm not totally sure how to find a vacuum leak, I'm guessing a vacuum gauge would be of help. I think I'm about ready to give up and take it to a local mechanic whom I trust.